The EPA’s move on Tuesday to undo the Obama administration’s signature climate change rule will almost certainly trigger an onslaught of lawsuits from environmental groups and many blue states that have been bracing for that action since President Donald Trump took office.

The agency said it had filed a notice with the Federal Register proposing to unravel the 2015 Clean Power Plan and will seek public input into that proposal over a 60-day period. But the EPA did not commit to promulgating a replacement policy to reduce greenhouse gas emissions, which environmentalists have said would lead them to sue to stop the repeal or force the agency to write a new policy.

The rule was the Obama administration’s most aggressive effort to cut carbon emissions from the U.S. power sector to combat climate change. The rule, which was stayed by the Supreme Court in February 2016 pending the outcome of a district court’s review, aims to reduce greenhouse gas emissions from existing power plants by 32 percent below 2005 levels by 2030.

Former Obama administration EPA administrator Gina McCarthy, who was at the center of finalizing the CPP, said in a news release that repealing the rule without a replacement would undermine efforts to combat climate change.

“A proposal to repeal the Clean Power Plan without any timeline or even a commitment to propose a rule to reduce carbon pollution, isn’t a step forward, it’s a wholesale retreat from EPA’s legal, scientific and moral obligation to address the threats of climate change.”

And writing a new rule could take months, even years to finalize, experts say.

7 Major Battles Ahead on the Environment

But Jeff Holmstead, a partner and environmental lawyer with DC firm Bracewell LLP, who participated in the court case challenging the rule, said the legal basis for repealing the rule is very strong.

“The tricky legal question is whether they replace it and what they replace it with,” Holmstead said, adding that if the EPA does not replace the Clean Power Plan, environmental groups will sue.

Indeed, Environmental Defense Fund president Fred Krupp said the group will continue to fight for the CPP, calling the move to repeal “a complete abdication of EPA’s legal responsibility to protect our children’s lungs from dangerous smokestack pollution” and their homes from climate-destabilizing extreme weather.

“A repeal-without-replace effort would completely ignore the vast toll that power plant pollution takes on our climate security, and would be an unconscionable abandonment of efforts to protect the health of our children and communities,” Krupp said.

Cleaning the slate?

Conservatives have long decried the CPP’s requirement that states develop plans to start cutting emissions by 2022 from plants within their borders, an issue the EPA Administrator Scott Pruitt cited as justification for repealing the policy.

“The Obama administration pushed the bounds of their authority so far with the CPP that the Supreme Court issued a historic stay of the rule, preventing its devastating effects to be imposed on the American people while the rule is being challenged in court,” Pruitt said in a news release. “We are committed to righting the wrongs of the Obama administration by cleaning the regulatory slate.”

As Oklahoma attorney general, Pruitt sued to overturn the rule.

Sen. Shelley Moore Capito, who hails from the coal state of West Virginia where the rule has been deemed a “war on coal,” lauded the move.

“It’s refreshing to see how committed the Trump administration is to pursuing a true all-of-the-above energy policy, and Administrator Pruitt’s announcement is another sign that America’s energy strategy is headed in the right direction,” Capito said in a news release.

The decline in coal production and demand is less due to regulations and more driven by market forces. Cheaper and cleaner burning natural gas has become more attractive than coal.

Thaddeus Lightfoot, a partner at the international law firm Dorsey and Whitney, focusing on environmental law, explained in a news release that despite the Trump administration’s claim, repealing the CPP will not save the coal industry.

“So long as natural gas remains relatively inexpensive, utilities will continue to move to this cheaper fuel as a substitute for coal while exploring the expansion of renewable fuels,” he said.

While Congress has no direct role to play on the fate of the CPP, Republican lawmakers have criticized it as a job killer and advocated the Trump administration prioritize gutting it.

Congressional Republicans aggressively used the Congressional Review Act to nullify several Obama administration regulations, but could not use that statute to undo the CPP because it was finalized before the cutoff period for CRA-eligible rules. The CRA allows Congress to undo regulations finalized within the last 60 legislative days of an administration.

Senate Majority Leader Mitch McConnell, who wrote a support letter to the court backing the states that challenged the CPP, has previously urged state governors against taking steps to prepare for the rule’s implementation.

“Any replacement rule will be done carefully, properly, and with humility, by listening to all those affected by the rule,” Pruitt said on Tuesday.

The Supreme Court has recognized greenhouse gases as dangerous pollutants, an argument environmental groups could use to back their demand for a new rule to regulate carbon emissions.

“In addition, any repeal of the Clean Power Plan must go through full notice-and-comment rulemaking and will be subject to judicial challenges once the rulemaking is complete,” Lightfoot said. “Indeed, many states are already taking steps to meet the carbon reduction targets set in the Clean Power Plan. A new proposed rule may slow these actions in some states but will not reverse the overall trend of reducing greenhouse gas emissions.”

Senate Environment and Public Works Committee Chairman John Barrasso of Wyoming welcomed the EPA’s move, saying the rule was unreasonable and unlawful.

“It would have hurt energy workers in Wyoming and harmed the state’s economy,” Barrasso said in a news release.

Democrats including Senate Environment and Public Works ranking member Thomas R. Carper of Delaware said they were angered by the move.

“Today, President Trump and Mr. Pruitt are on the wrong side of history,” Carper said. “They are creating their own reality, complete with rigged science and math, to justify doing nothing in the face of the greatest environmental challenge of our lifetime. That is not leadership.”